"Rapid changes already underway to the Earth's climate, ecosystems and land cover threaten the health of billions, undermining key human life-support systems and threatening the core foundations of healthy communities worldwide, according to a new report released Wednesday.

The disruption represents the greatest public health challenge of the 21st century and leaves poor populations mostly in developing nations most vulnerable -- even though they contribute the least to many of the problems. The report was published jointly by the Worldwatch Institute and the United Nations Foundation, two nonprofit organizations working on global policy."